Starts, dies, starts, dies, starts dies, then runs
12-08-2020, 05:34 PM
#1
Race Director
Thread Starter
Starts, dies, starts, dies, starts dies, then runs
Last couple of times I moved it, the vette starts, Idles fine for a second, then dies. This repeats a few times till I can get it moving (stick car). Once moving, it seems fine. Doesn't run well enough to pull it...until a bit warm. But, it idles fine for a bit.
Last summer, it started having problems "bucking" when cold. I have a descreened MAF on my 383...since 2010. It's tuned with that MAF. I finally tried a backup (used OEM screened) MAF...that I also had. It seemed to solve the problem...though it bucked ONCE the first use. Fine after that.
Figured I'd get a FP gauge from AutoZone...to see where that's at...but don't expect problems. Installed a new FP in 2013. Plus, if the FP is bad, why would it start? If the regulator is bad, I'm assuming pressure would be a bit too high...and not cause this new symptom.
If it's a vacuum leak, I'm surprised it will start running fine after 3-5 starts!
Hints on diagnostic tests/procedures you'd do?
FYI: It's an 89 modified to a 383. Stock electronics/sensors still in play. If it was my old '68 GTO...I'd be looking at the choke, but this is tuned and has been fine for years.
Last summer, it started having problems "bucking" when cold. I have a descreened MAF on my 383...since 2010. It's tuned with that MAF. I finally tried a backup (used OEM screened) MAF...that I also had. It seemed to solve the problem...though it bucked ONCE the first use. Fine after that.
Figured I'd get a FP gauge from AutoZone...to see where that's at...but don't expect problems. Installed a new FP in 2013. Plus, if the FP is bad, why would it start? If the regulator is bad, I'm assuming pressure would be a bit too high...and not cause this new symptom.
If it's a vacuum leak, I'm surprised it will start running fine after 3-5 starts!
Hints on diagnostic tests/procedures you'd do?
FYI: It's an 89 modified to a 383. Stock electronics/sensors still in play. If it was my old '68 GTO...I'd be looking at the choke, but this is tuned and has been fine for years.
Last edited by GREGGPENN; 12-08-2020 at 05:44 PM.
12-08-2020, 07:17 PM
#2
Safety Car
Have you taken a look at your Coolant Temperature Sensor's signal? If your engine's CTS is feeding it bad data it can make the fuel system do strange things. If it thinks the engine is warmer than it really is then you could have starting problems related to the erroneous data.
If the CTS tells the ECM that it is colder than the engine really is the ECM will enrich the fuel mixture due to the "colder" temperatures. The later scenario is where it seems like the Choke is stuck "on" in the old days.
Read the signal going to the ECM using a scanner if available. I use a harness that piggybacks onto the CTS power plug and lets me see the signal being sent. Sometimes they just need their connections cleaned but they do have a habit of going bad.
How old is your Oxygen sensor? On the 1989 you should have single O2. The life span of the O2 was designed to be 24 Months or 50K miles. OBD2 cars can double it and even more. When an O2 starts to go bad it can make some strange problems. When the Oxygen Sensors fail for good the car will be left in "Limp Mode" and not be very drive able.
If the CTS tells the ECM that it is colder than the engine really is the ECM will enrich the fuel mixture due to the "colder" temperatures. The later scenario is where it seems like the Choke is stuck "on" in the old days.
Read the signal going to the ECM using a scanner if available. I use a harness that piggybacks onto the CTS power plug and lets me see the signal being sent. Sometimes they just need their connections cleaned but they do have a habit of going bad.
How old is your Oxygen sensor? On the 1989 you should have single O2. The life span of the O2 was designed to be 24 Months or 50K miles. OBD2 cars can double it and even more. When an O2 starts to go bad it can make some strange problems. When the Oxygen Sensors fail for good the car will be left in "Limp Mode" and not be very drive able.
12-09-2020, 02:24 PM
#3
Race Director
Thread Starter
Have you taken a look at your Coolant Temperature Sensor's signal? If your engine's CTS is feeding it bad data it can make the fuel system do strange things. If it thinks the engine is warmer than it really is then you could have starting problems related to the erroneous data.
If the CTS tells the ECM that it is colder than the engine really is the ECM will enrich the fuel mixture due to the "colder" temperatures. The later scenario is where it seems like the Choke is stuck "on" in the old days.
If the CTS tells the ECM that it is colder than the engine really is the ECM will enrich the fuel mixture due to the "colder" temperatures. The later scenario is where it seems like the Choke is stuck "on" in the old days.
12-09-2020, 11:22 PM
#5
Might be a weak fuel pump.
You say it takes 3-5x starting the vehicle then it runs. Because it's a weak pump, it takes extra effort to pressurize the fuel lines.
Have you tried going really fast? When I had a weak fuel pump, I couldn't go past like 40 mph.
Instead of buying all the tools necessary to check fuel pressure, you might do one of the following:
1. Replace the fuel filter (might be clogged)
2. Get a cheap fuel pump from ebay ($20) and just change that bad boy out. If your problem goes away, then you can buy a good-quality fuel pump and replace it. Replacing the fuel pump isn't difficult, 15 minute job once you're used to all the steps.
My two cents.
You say it takes 3-5x starting the vehicle then it runs. Because it's a weak pump, it takes extra effort to pressurize the fuel lines.
Have you tried going really fast? When I had a weak fuel pump, I couldn't go past like 40 mph.
Instead of buying all the tools necessary to check fuel pressure, you might do one of the following:
1. Replace the fuel filter (might be clogged)
2. Get a cheap fuel pump from ebay ($20) and just change that bad boy out. If your problem goes away, then you can buy a good-quality fuel pump and replace it. Replacing the fuel pump isn't difficult, 15 minute job once you're used to all the steps.
My two cents.
Last edited by Sergio Lane; 12-09-2020 at 11:25 PM.
12-11-2020, 04:05 AM
#6
Race Director
Thread Starter
No need to buy tools. AutoZone lends FP testers for free. I need to hookup my laptop and check the temp reading. I think that's more likely considering I'm running a fairly new Walbro FP.
Unplugging the temp sensor seems like that would cause it's own set of problems. Gotta wonder how table table would work if it didn't at least know the engine temp!
While on the subject of temp and the choke "circuit", I've always wanted to make sure I understood how cold enrichment functions. This has been my guess...
1) After any delay (mine is set to zero), Fuel PW table tells how much (%) raw fuel to "inject" for the 1st three revolutions...based on % of PW?
2) Startup Enrichment vs Coolant Temp table sets percentage enrichment
3) Startup Enrichment Decay pulls out percentage of [enrichment] fuel for each X seconds listed in table
4) Normal mixture is obtained when # 3 [essencially] pulls all enrichment OR Hot/Warm/Cold closed loop timer ends.
Any chance I got this right?
Unplugging the temp sensor seems like that would cause it's own set of problems. Gotta wonder how table table would work if it didn't at least know the engine temp!
While on the subject of temp and the choke "circuit", I've always wanted to make sure I understood how cold enrichment functions. This has been my guess...
1) After any delay (mine is set to zero), Fuel PW table tells how much (%) raw fuel to "inject" for the 1st three revolutions...based on % of PW?
2) Startup Enrichment vs Coolant Temp table sets percentage enrichment
3) Startup Enrichment Decay pulls out percentage of [enrichment] fuel for each X seconds listed in table
4) Normal mixture is obtained when # 3 [essencially] pulls all enrichment OR Hot/Warm/Cold closed loop timer ends.
Any chance I got this right?
12-11-2020, 05:57 PM
#7
Safety Car
I would not rule out Low Voltage at the Fuel Pump or the Fuel Pump Relay. I once saw a 2 volt drop at the fuse panel coming from the Battery itself. It was a corroded post that fed SEVEN Fusible Links their power. Before I fixed the Post in question the Fuel Pressure Pump was not happy running at all and you could hear it barely working. After repairing the corrosion the Inside of the Corvette was Brighter everything including the stereo was working properly. The most important change was the car would start right up and run great with proper voltage everywhere.
I am not able to be of much help with your questions regarding how our ECM's do their job regarding Cold Starting. That darn CTS is critical to the entire engines software. They use that signal in many important computations and it affects the Air/Fuel ratio as an example.
Recently I installed a Holley Stealth Sniper on a C3 and setting up the Computer is not hard, fortunately the system is "Self-Learning" as I would mess it up for sure. But the Holley system allows to you to program the car to get extra fuel, you can do it manually or let the system do it itself. I am in the "Self-Learning Mode" myself with setting up Fuel Tables and such. I love the versatility of the Holley Stealth Sniper and it's Software package.
I am not able to be of much help with your questions regarding how our ECM's do their job regarding Cold Starting. That darn CTS is critical to the entire engines software. They use that signal in many important computations and it affects the Air/Fuel ratio as an example.
Recently I installed a Holley Stealth Sniper on a C3 and setting up the Computer is not hard, fortunately the system is "Self-Learning" as I would mess it up for sure. But the Holley system allows to you to program the car to get extra fuel, you can do it manually or let the system do it itself. I am in the "Self-Learning Mode" myself with setting up Fuel Tables and such. I love the versatility of the Holley Stealth Sniper and it's Software package.
09-04-2021, 04:22 AM
#8
Race Director
Thread Starter
When doing a search, it's always nice to find solutions at the end of the thread. After finishing a slew of other spring/summer chores, I finally found the time to fix my car. Here's what happened.
First, I tried connecting my laptop to the ECM via ALDL. Never got it to connect. Tried multiple days -- several times each. (I have two ALDL cables and thought I was using the right one...plus I couldn't find the other.) House prep/painting, shingles, daughter moving, and lots of other things intervened. Plus, I was sure it would be the CTS (as might be evident from my comments in prior posts above.)
Anyway, step one (for CTS replacement) included draining the coolant and performing a complete flush as part of the process. So, I read up on that since it had been awhile. Man...there a LOT of opinions on here! LOL Oh wait...the internet too.
Deciding how to perform a complete flush was a chore in itself. I finally decided to pull the TB, then stat, then flush, then fill with distilled water.
Before I did that, the battery died this spring. I bought a new one, then another (to get more cranking amps), then a trickle charger, returned that, then verified the battery would stay charged over a couple weeks, etc... While I had the battery out, I cleaned the posts BEHIND the battery mentioned above. I also decided to buy new MAF relays -- since the car mysteriously shut down on the hwy (for an instant) last fall. Given some thought, it seems likely the MAF relay (if not ECM or distributor) lost continuity for a second. I was hoping for the relay -- given how they work. AND, that I was nearing the end of my battery's life.
Bottom line: I replaced the MAF relays, cleaned the power distribution posts, and installed a new CTS (during the coolant flush). BEFORE I did the later, the car started fine -- to pull it out on the driveway. So....it's quite possible the problem was identified by Mr. McCloskey in his post above. You know...his post about the post! LOL The bottom line is it starts fine now...so the problem is solved. I have the feeling it was the post judging by it's less-than perfect appearance. (Not saying it was horrible after 32 years...but it didn't look new either!)
Low battery voltage PLUS a bad post seems even more likely -- given the voltage it was producing before I finally gave up on the old battery. I just assumed anything sufficient to turn the starter was enough to run the electronics. Probably a bad assumption for a car of it's age.
Anyway, the dash looks brighter and I haven't seen it fluctuate in brightness -- yet. Since I saw that a couple of times before "service", Christopher's comments became more relevant. Thank you Chris!
I was a bit concerned about the age of the fuel -- given that it sat for 8 months -- but it seems to run fine. I've finally gone through that tank and filled it again so I'm glad the fuel is flushed too! Too bad I do less and less night driving after Covid changed habits and store hours. I've only driven at night once -- so it might take quite awhile before confirming ALL the pre-service gremlins have been cured! I'm pumped though!
By the way...the first time I actually got out and drove it after months of sitting, I noticed the second ALDL cable under the front of the passenger seat. DUMB ***....Why did I leave it there! Seems more likely that I used the bad cable. Man it sucks if you can't connect to the ECM!!! Luckily, lots of great advice comes out of this forum. I doubt I replaced anything that didn't require it.
FWIW, The CTS and MAF relays were last replaced in 2007 -- 3 years before I swapped blocks and installed the 383. (I reused those electronics IIRC). The last coolant flush was about 2016? Sadly, I've driven it less than 10k since then. Rehabbing a 1975 house really changes a guy's priorities! Being semi-retired does too. Point being, the coolant still looked bright green and new.
Now I'm onto the next step...getting the A/C to work again. You guys already know that because I posted about that a couple weeks ago. Parts for that are in hand...All I need is an R12 manifold gauge (set). Or...buy the 134a fittings and use a newer one....until it's charged up...and working again. (I have one of those tire-gauge style gauges...so I'll be able to tell if my seal repair doesn't work (assuming I borrow GOOD gauges to perform the freon load).
Anyway...thanks to all who contributed to this thread!!!!
First, I tried connecting my laptop to the ECM via ALDL. Never got it to connect. Tried multiple days -- several times each. (I have two ALDL cables and thought I was using the right one...plus I couldn't find the other.) House prep/painting, shingles, daughter moving, and lots of other things intervened. Plus, I was sure it would be the CTS (as might be evident from my comments in prior posts above.)
Anyway, step one (for CTS replacement) included draining the coolant and performing a complete flush as part of the process. So, I read up on that since it had been awhile. Man...there a LOT of opinions on here! LOL Oh wait...the internet too.
Deciding how to perform a complete flush was a chore in itself. I finally decided to pull the TB, then stat, then flush, then fill with distilled water. Before I did that, the battery died this spring. I bought a new one, then another (to get more cranking amps), then a trickle charger, returned that, then verified the battery would stay charged over a couple weeks, etc... While I had the battery out, I cleaned the posts BEHIND the battery mentioned above. I also decided to buy new MAF relays -- since the car mysteriously shut down on the hwy (for an instant) last fall. Given some thought, it seems likely the MAF relay (if not ECM or distributor) lost continuity for a second. I was hoping for the relay -- given how they work. AND, that I was nearing the end of my battery's life.
Bottom line: I replaced the MAF relays, cleaned the power distribution posts, and installed a new CTS (during the coolant flush). BEFORE I did the later, the car started fine -- to pull it out on the driveway. So....it's quite possible the problem was identified by Mr. McCloskey in his post above. You know...his post about the post! LOL The bottom line is it starts fine now...so the problem is solved. I have the feeling it was the post judging by it's less-than perfect appearance. (Not saying it was horrible after 32 years...but it didn't look new either!)
Low battery voltage PLUS a bad post seems even more likely -- given the voltage it was producing before I finally gave up on the old battery. I just assumed anything sufficient to turn the starter was enough to run the electronics. Probably a bad assumption for a car of it's age.
Anyway, the dash looks brighter and I haven't seen it fluctuate in brightness -- yet. Since I saw that a couple of times before "service", Christopher's comments became more relevant. Thank you Chris!
I was a bit concerned about the age of the fuel -- given that it sat for 8 months -- but it seems to run fine. I've finally gone through that tank and filled it again so I'm glad the fuel is flushed too! Too bad I do less and less night driving after Covid changed habits and store hours. I've only driven at night once -- so it might take quite awhile before confirming ALL the pre-service gremlins have been cured! I'm pumped though!
By the way...the first time I actually got out and drove it after months of sitting, I noticed the second ALDL cable under the front of the passenger seat. DUMB ***....Why did I leave it there! Seems more likely that I used the bad cable. Man it sucks if you can't connect to the ECM!!! Luckily, lots of great advice comes out of this forum. I doubt I replaced anything that didn't require it.
FWIW, The CTS and MAF relays were last replaced in 2007 -- 3 years before I swapped blocks and installed the 383. (I reused those electronics IIRC). The last coolant flush was about 2016? Sadly, I've driven it less than 10k since then. Rehabbing a 1975 house really changes a guy's priorities! Being semi-retired does too. Point being, the coolant still looked bright green and new.
Now I'm onto the next step...getting the A/C to work again. You guys already know that because I posted about that a couple weeks ago. Parts for that are in hand...All I need is an R12 manifold gauge (set). Or...buy the 134a fittings and use a newer one....until it's charged up...and working again. (I have one of those tire-gauge style gauges...so I'll be able to tell if my seal repair doesn't work (assuming I borrow GOOD gauges to perform the freon load).
Anyway...thanks to all who contributed to this thread!!!!
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ctmccloskey (09-06-2021)